A detailed model for transient liquid flow in heat pipe wicks

Transient liquid flow in a low-temperature, homogeneous wick heat pipe is investigated experimentally and analytically for pulsed heat load conditions. The continuous distribution of the liquid in the wick is modeled, where previous models had assumed a uniformly saturated structure. A heat pipe with beryllium walls was used to obtain transient measurements of the saturation distribution in the wick structure using x-ray radiography. Analytical and experimental results are presented for the axial liquid distribution in the wick as a function of time. Transient liquid distributions for the model and experiment compare favorably. These results show that significant reductions in saturation may occur in the evaporator region for higher heat loads. These reductions affect the wick-flow properties and must be included in the liquid-flow analysis.